The present invention is directed to an arrangement and method for measuring speed or geometry of moving objects with the registration of range images (highlight images) on the basis of measurements of the running time of light.
The speed of an individual object as well as the characterization of the object are necessary for automatic monitoring of vehicle traffic as well as of general material transport. In traffic monitoring, this means the exact measurement of the vehicle speed as well as, for example, distinguishing between passenger vehicles, trucks or motorcycles. In material transport with a conveyor belt, the total volume conveyed per unit time and, given a constant specific weight, the quantity (i.e., the overall weight) can both be automatically determined by constant acquisition of the speed as well as the cross-section of the conveyed material.
When only the speed of vehicles is measured, various methods are currently available such as radar or infrared systems that measure in a passive way. These systems essentially satisfy the demands that are made of them. However, it is extremely disadvantageous that measurement must be carried out in or opposite the direction of travel of the objects, and that a simultaneous characterization of the moving object can be realized only to an extremely limited extent.
A method is known wherein a range image (distance image, height image) is acquired by a CMOS image sensor having an extremely short integration time (for example 30 ns) as well as a laser pulse illumination of the object. The main employment of these methods has previously been monitoring rooms, particularly monitoring the interior of a vehicle.
The present invention is based on the need to make an arrangement and a method available for an exact speed measurement as well as an acquisition of the geometry of moving objects with a single system.
These and other needs are achieved by the present invention through an arrangement for measuring at least the speed or surface shape of moving objects, or a combination thereof, based on measurements of the travel time and intensity of light emitted from a light source and reflected back by the moving objects. The arrangement includes at least one light source configured to illuminate the moving objects with light pulses. In addition, at least two optical semiconductor sensor lines are positioned in the region of the at least one light source and are comprised of a plurality of sensor elements for sensing light emitted from the at least one light source that is reflected by the moving objects and the moving objects background across which the moving objects travel. The at least two optical semiconductor sensor lines are spaced a predetermined distance relative to one another and are disposed parallel to one another. Further, the sensor lines are arranged traverse to a travel direction of the moving objects. The arrangement further includes a controller to calculate range profiles of the moving objects based on measured travel time and intensity of light emitted from the light source and reflected back by either the moving objects or the moving object background. The controller then is able to derive a surface shape of the moving objects based on the calculated range profiles.
According to another aspect of the present invention, a method is provided to determine either the speed or surface shape of moving objects, or combination thereof, based on measurements of travel time of light emitted from a light source and reflected back by the moving objects. Included are the step of emitting at least one light pulse from the light source and then sensing light of the light pulse reflected from one of a moving object or a moving object background using at least two optical semiconductor sensor lines positioned in the region of the light source. The optical semiconductor lines are each comprised of a plurality of sensor elements. The travel time and intensity light emitted from the light source is then measured and range profiles are calculated for moving objects based on measured travel time and intensity of light that is emitted and reflected back by at least one of the moving objects or the moving object background. A first calculated range profile of the moving object background where no moving object is present is first calculated and then compared to a subsequently calculated range profile of the moving object as it travels across the moving object background. From this at least one cross-sectional profile is determined based on a difference between the first calculated range profile and at least one subsequently calculated range profile when the moving object is present.
The invention is based on the perception that the above need can be met based on the principle of producing range images or object profiles with measurements of the running time of light. To this end, two opto-electronic semiconductor sensor lines are utilized in combination with an illumination, wherein surface parts of objects are illuminated, and range images are supplied by the opto-electronic semiconductor sensor lines by evaluating the running times of light from the illumination to the object. The use of two spaced semiconductor sensor lines enables a short-time offset registration of the same surface profile or of the same location at the object, wherein, given a known distance between the sensor lines or between an illuminated stripe on a background or reference plane, the speed of the object is calculated. A plurality of cross-sectional areas of the moving object are first registered, their sequence describing the longitudinal profile of the object. A measurement of the speed and a registration of the geometry of the measured object can thus be realized overall with a single system.
For increasing the readout speed at the electrical side of the semiconductor sensor lines, it is advantageous to be able to freely select the sensor elements. As a result, a relatively slow serial readout of sensor lines is avoided. The use of CMOS technology by employing CMOS components in the semiconductor sensor lines affords an especially compact structure, wherein a particular advantage results from integrating both light lines on one semiconductor component.
When the number of sensor elements with which a semiconductor line is constructed is limited to, for example, 32, then the individual sensor elements representing the semiconductor sensor lines are of adequate size and exhibit corresponding light sensitivity. Correspondingly, the power of the illumination side can be kept low.
Over and above this, such a light-sensitive semiconductor line can be read out in an extremely short time, for example in a few microseconds. It is advantageous to design the light sources located in the proximity of the semiconductor sensor lines as modulatable laser diodes, for example laser diodes that can be frequency-modulated or amplitude-modulated. For adhering, to laser safety stipulations, for example, a plurality of light sources can be employed, these respectively partially illuminating an object. The light sources are thereby preferably serially activated, wherein partial surface regions are illuminated and correspondingly interpreted at the semiconductor sensor lines. The most advantageous arrangement of the semiconductor sensor lines relative to the objects is comprised in their perpendicular alignment relative to the travel direction of the objects given a pass above or to the side of the object. The illumination, which is arranged extremely close to the semiconductor sensor lines, illuminates a line-like region on the object background that approximately corresponds to the coverage area of the semiconductor sensor lines. The illumination and acquisition areas to be allocated to the respective sensor line are advantageously spaced one meter apart. The two areas are aligned mutually parallel corresponding to the semiconductor sensor lines. When vehicles that move on a travel lane are to be measured, then the width of the travel lane should be completely illuminated.
The structure of the semiconductor sensor lines provides resolution using individual element areas that are arranged in a line. Thus, correspondence between individual sensor elements of the semiconductor sensor line and a corresponding location in the line-like coverage area of the semiconductor line on the object background or on the object exists. When short-time integration is advantageously selected as the measuring method for the running time of light, then a specific measuring method is comprised in measuring or integrating the light received up to that point in time at the semiconductor sensor elements at two integration times, one occurring shortly after the other. In order to be able to implement the two integration times parallel in time and, thus, in order to shorten the measuring time, the individual sensor elements of the semiconductor sensor lines are redundantly designed such that an identical optical charging occurs. This is effected by a meshing of electrically sensitive, light-sensitive surfaces on one sensor element.
For determining the surface shape of vehicles, a distance profile of the background having an object located thereon is registered after the registration of a distance profile of the background. The differences between registration before and during when the object moves across the background yield a plurality of profiles of the object. The area of the cross-section can be respectively calculated from these cross-sectional profiles. The longitudinal profile of the moving object results in the sequence of cross-sectional areas. By employing two semiconductor sensor lines having a predetermined spacing from one another, both the object shape as well as the speed of the object can be identified. One particular advantage is that an object can be categorized on the basis of these data. By comparison to a respective pattern, for example, recognition can be made between whether the moving object is a matter of a person, a motorcycle, a passenger vehicle or a truck.
Additional advantages and novel features of the invention will be set forth, in part, in the description that follows and, in part, will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.